Casting is the process of trying out talent to book on a particular project for TV, Film, Commercials or Theatre. When a performer wishes to be cast in a production, that performer will display their talents to a casting director or producer of the project. The casting director is the person running the try-out and will have a heavy impact on choosing the right talent for the production.
When attending a casting, always bring your headshot and resume with you. Arrive thirty minutes before your scheduled performance and be prepared, either by memorizing the song you are singing or knowing the lines you will be acting. Be polite and professional to the casting people involved in the tryout and never ask a casting director if you got the part; don't call them, they'll call you. If you attend a casting session pre-pared, professional and excited to perform, you are already a success.